[RFCv2] mm: page allocation for less fragmentation

Gioh Kim
2015-03-25T02:38:45Z

My driver allocates more than 40MB pages via alloc_page() at a time and
maps them at virtual address. Totally it uses 300~400MB pages.

If I run a heavy load test for a few days in 1GB memory system, I cannot allocate even order=3 pages
because-of the external fragmentation.

I thought I needed a anti-fragmentation solution for my driver.
But there is no allocation function that considers fragmentation.
The compaction is not helpful because it is only for movable pages, not unmovable pages.

This patch proposes a allocation function allocates only pages in the same pageblock.

I tested this patch like following:

1. When the driver allocates about 400MB and do "cat /proc/pagetypeinfo;cat /proc/buddyinfo"

Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
Node 0, zone Normal, type Unmovable 3864 728 394 216 129 47 18 9 1 0 0
Node 0, zone Normal, type Reclaimable 902 96 68 17 3 0 1 0 0 0 0
Node 0, zone Normal, type Movable 5146 663 178 91 43 16 4 0 0 0 0
Node 0, zone Normal, type Reserve 1 4 6 6 2 1 1 1 0 1 1
Node 0, zone Normal, type CMA 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone Normal, type Isolate 0 0 0 0 0 0 0 0 0 0 0

Number of blocks type Unmovable Reclaimable Movable Reserve CMA Isolate
Node 0, zone Normal 135 3 124 2 0 0
Node 0, zone Normal 9880 1489 647 332 177 64 24 10 1 1 1

2. The driver frees all pages and allocates pages again with alloc_pages_compact.
This is a kind of compaction of the driver.
Following is the result of "cat /proc/pagetypeinfo;cat /proc/buddyinfo"

Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
Node 0, zone Normal, type Unmovable 8 5 1 432 272 91 37 11 1 0 0
Node 0, zone Normal, type Reclaimable 901 96 68 17 3 0 1 0 0 0 0
Node 0, zone Normal, type Movable 4790 776 192 91 43 16 4 0 0 0 0
Node 0, zone Normal, type Reserve 1 4 6 6 2 1 1 1 0 1 1
Node 0, zone Normal, type CMA 0 0 0 0 0 0 0 0 0 0 0
Node 0, zone Normal, type Isolate 0 0 0 0 0 0 0 0 0 0 0

Number of blocks type Unmovable Reclaimable Movable Reserve CMA Isolate
Node 0, zone Normal 135 3 124 2 0 0
Node 0, zone Normal 5693 877 266 544 320 108 43 12 1 1 1

I found that fragmentation is decreased.

This patch is based on 3.16. It is not change any code so that it can apply to any version.

Changelog since v1:
- change argument of page order into page count

Signed-off-by: Gioh Kim <gioh.kim@lge.com>
---
mm/page_alloc.c | 167 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 167 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 86c9a72..e269030 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6646,3 +6646,170 @@ void dump_page(struct page *page, const char *reason)
dump_page_badflags(page, reason, 0);
}
EXPORT_SYMBOL(dump_page);
+
+static unsigned long alloc_freepages_block(unsigned long start_pfn,
+ unsigned long end_pfn,
+ int count,
+ struct list_head *freelist)
+{
+ int total_alloc = 0;
+ struct page *cursor, *valid_page = NULL;
+
+ cursor = pfn_to_page(start_pfn);
+
+ /* Isolate free pages. */
+ for (; start_pfn < end_pfn; start_pfn++, cursor++) {
+ int alloc, i;
+ struct page *page = cursor;
+
+ if (!pfn_valid_within(start_pfn))
+ continue;
+
+ if (!valid_page)
+ valid_page = page;
+ if (!PageBuddy(page))
+ continue;
+
+ if (!PageBuddy(page))
+ continue;
+
+ /* allocate only low-order pages */
+ if (page_order(page) >= 3) {
+ start_pfn += (1 << page_order(page)) - 1;
+ cursor += (1 << page_order(page)) - 1;
+ continue;
+ }
+
+ /* Found a free pages, break it into order-0 pages */
+ alloc = split_free_page(page);
+
+ total_alloc += alloc;
+ for (i = 0; i < alloc; i++) {
+ list_add(&page->lru, freelist);
+ page++;
+ }
+
+ if (total_alloc >= count)
+ break;
+
+ if (alloc) {
+ start_pfn += alloc - 1;
+ cursor += alloc - 1;
+ continue;
+ }
+ }
+
+ return total_alloc;
+}
+
+static int rmqueue_compact(struct zone *zone, int nr_request,
+ int migratetype, struct list_head *freepages)
+{
+ unsigned int current_order;
+ struct free_area *area;
+ struct page *page;
+ unsigned long block_start_pfn; /* start of current pageblock */
+ unsigned long block_end_pfn; /* end of current pageblock */
+ int total_alloc = 0;
+ unsigned long flags;
+ struct page *next;
+ int to_free = 0;
+ int nr_remain = nr_request;
+ int loop_count = 0;
+
+ spin_lock_irqsave(&zone->lock, flags);
+
+ /* Find a page of the appropriate size in the preferred list */
+ current_order = 0;
+ page = NULL;
+ while (current_order <= pageblock_order) {
+ int alloc;
+
+ /* search all possible pages in each list? */
+ if (loop_count > (zone->managed_pages / (1 << current_order)))
+ goto next_order;
+ loop_count++;
+
+ area = &(zone->free_area[current_order]);
+
+ if (list_empty(&area->free_list[migratetype]))
+ goto next_order;
+
+ page = list_entry(area->free_list[migratetype].next,
+ struct page, lru);
+
+ /*
+ * check migratetype of pageblock again,
+ * some pages can be set as different migratetype
+ * by rmqueue_fallback
+ */
+ if (get_pageblock_migratetype(page) != migratetype)
+ continue;
+
+ block_start_pfn = page_to_pfn(page) & ~(pageblock_nr_pages - 1);
+ block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
+ zone_end_pfn(zone));
+
+ alloc = alloc_freepages_block(block_start_pfn,
+ block_end_pfn,
+ nr_remain,
+ freepages);
+
+ total_alloc += alloc;
+ nr_remain -= alloc;
+
+ /*
+ * alloc == 0: free buddy block is found but it is too big
+ * or free buddy block is not valid page.
+ * Try next order.
+ */
+ if (alloc == 0)
+ goto next_order;
+
+ if (nr_remain <= 0)
+ break;
+
+next_order:
+ current_order++;
+ loop_count = 0;
+ }
+ __mod_zone_page_state(zone, NR_ALLOC_BATCH, -total_alloc);
+ __count_zone_vm_events(PGALLOC, zone, total_alloc);
+
+ spin_unlock_irqrestore(&zone->lock, flags);
+
+ list_for_each_entry_safe(page, next, freepages, lru) {
+ if (to_free >= nr_request) {
+ list_del(&page->lru);
+ atomic_dec(&page->_count);
+ __free_pages_ok(page, 0);
+ }
+ to_free++;
+ }
+
+ list_for_each_entry(page, freepages, lru) {
+ arch_alloc_page(page, 0);
+ kernel_map_pages(page, 1, 1);
+ }
+ return total_alloc < nr_request ? total_alloc : nr_request;
+}
+
+int alloc_pages_compact(gfp_t gfp_mask, int nr_request,
+ struct list_head *freepages)
+{
+ enum zone_type high_zoneidx = gfp_zone(gfp_mask);
+ struct zone *preferred_zone;
+ struct zoneref *preferred_zoneref;
+
+ preferred_zoneref = first_zones_zonelist(node_zonelist(numa_node_id(),
+ gfp_mask),
+ high_zoneidx,
+ &cpuset_current_mems_allowed,
+ &preferred_zone);
+ if (!preferred_zone)
+ return 0;
+
+ return rmqueue_compact(preferred_zone, nr_request,
+ allocflags_to_migratetype(gfp_mask), freepages);
+}
+EXPORT_SYMBOL(alloc_pages_compact);
--
1.7.9.5